The plane and the conveyor belt

February 9, 2006 · 14 comments

I saw this on kottke and I've been thinking/reading about it since. Here's the question:

A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?

I talked about it with a couple of people at dinner and I've been reading other people's thoughts on it, and I've concluded that the plane will take off (my initial reaction was of course it won't take off, you idiot). I'll follow up tomorrow with how I reached this conclusion.

What do you think? Leave a comment.

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  • Laina

    of course it wont take off. what a ridiculously posed question.

  • kim

    i'm gonna go with a negative on that one.

  • ps

    ok.
    the plane will take off.

    the plane will have a ground speed (how fast the wheels are moving) that is a completely different from normal take-off, but it can still acheive sufficient airspeed for take-off. ((i also think the runway needs to be a different length…although i don’t know if it would need to be longer or actually shorter)).

    i could attempt to explain the physics, but won’t…cause i’m still not great at physics, but:
    planes are not like cars. a car moves forward because the wheels (in contact with the ground) provide forward force/motion. with a plane, the forward force/motion is created by the engine/propeller. the wheels on a plane are just there so the plane can roll, and so it can brake. the only effect wheels can have on a plane would be to brake so hard that the plane doesn’t move.

    in closing: the plane will take-off, and the wheels will be spinning uncontrollably beneath it…but the plane will still move forward (maybe think of it like a plane w/ skis that takes off of snow/water).

    feel free to ask questions, but i make zero guarantees about my ability to answer them.

  • mom

    I think it will take off because of the air draft created which is what allows a plane to lift off

  • Jonathan

    Ya, the plane will definitely take off just or nearly as easily as normal.

  • NATHAN

    impossible, the plane wouldn’t be moving forward at all. like standing on a trend mill, you expend energy but you don’t go anywhere. (however i could be reading the question wrong)

  • Nick

    The plane will not fly. There is no way for it to gain the lift it needs. The wheels are the only point of contact to the “ground” and if they are spinning in the opposite direction, there will be no forward momentum. Their has to be forward momentum to create the lift over the wings. If the speeds are matched perfectly there will be no wind or current of air flowing over the wings, i.e. the plane will not move. Forward momentum is needed to gain flight. No way this thing will fly.

  • Alisha

    I’d have to agree w/ Nick on this one.

  • Dad

    I’m with the no crowd. Even though the belt is moving, the plane is not, therefore no wind to creat the air flow to lift the plane.

    Dad

  • Luke

    definitely not gonna take off. if the conveyor belt is moving opposingly, at an equal speed, the plane will be at a standstill. Thus, there will be no airflow created. No airflow, no draft, to take-off. And it’s a pretty huge waste of gas.

  • http://polyspline.com/blog/ Ryan Tow

    No way. Plane sits still. If engines of plane push aircraft to speed approaching X, and conveyor belt applies negative velocity of -X, the aircraft will essentially remain in place. Zero airspeed.

    OTOH – apply a wind force equal to takeoff airspeed blowing towards the plane, parallel with runway. Apply a force to plane sufficient to keep it from blowing backwards. Plane will become airborne as windspeed approaches required takeoff airspeed.

  • Molly

    why does it matters either way? clearly a plane is never going to take off from a moving conveyer belt anyways. or will it? maybe i’m just behind in the math and science breakthrough news data.

    quick ask me and English question. i bet i can give you an answer to one of those!

  • Molly

    and by “and English question” i mean “an English question.”

    shoot…maybe i won’t do so hot in that area either….

  • Lisa

    Well ill throw a comment on since i am a pilot and go to school for flight training. no, there is no airflow over the wings to create the high pressure underneath and low on top that creates lift because the aircraft is motionless, only the wheels are moving